U.S. patent application number 16/341875 was filed with the patent office on 2019-08-08 for direct singlet capture organic molecules with short emission decay time and application thereof in optoelectronic devices.
This patent application is currently assigned to SICHUAN KNOWLEDGE EXPRESS INSTITUTE FOR INNOVATIVE TECHNOLOGIES CO., LTD. The applicant listed for this patent is SICHUN KNOWLEDGE EXPRESS INSTITUTE FOR INNOVATIVE TECHNOLOGIES CO., LTD. Invention is credited to Rafal CZERWIENIEC, Larisa MATARANGA-POPA, Hartmut YERSIN.
Application Number | 20190245151 16/341875 |
Document ID | / |
Family ID | 62978785 |
Filed Date | 2019-08-08 |
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United States Patent
Application |
20190245151 |
Kind Code |
A1 |
YERSIN; Hartmut ; et
al. |
August 8, 2019 |
DIRECT SINGLET CAPTURE ORGANIC MOLECULES WITH SHORT EMISSION DECAY
TIME AND APPLICATION THEREOF IN OPTOELECTRONIC DEVICES
Abstract
The invention relates to novel pure organic emitter molecules
and optoelectronic devices containing these organic emitter
molecules. According to the invention, in the optoelectronic
device, after the excitation of an organic molecule, relaxation and
intersystem crossing processes also result from the almost
isoenergetic charge transfer triplet state (.sup.3CT) for the
direct rapid occupation and emission of the charge transfer singlet
state (.sup.1CT), so that a .sup.1CT.fwdarw.S.sub.0 fluorescence
occurs without a thermal activation.
Inventors: |
YERSIN; Hartmut; (Sinzing,
DE) ; MATARANGA-POPA; Larisa; (Regensburg, DE)
; CZERWIENIEC; Rafal; (Obertraubling, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SICHUN KNOWLEDGE EXPRESS INSTITUTE FOR INNOVATIVE TECHNOLOGIES CO.,
LTD |
Meishan, Sichuan |
|
CN |
|
|
Assignee: |
SICHUAN KNOWLEDGE EXPRESS INSTITUTE
FOR INNOVATIVE TECHNOLOGIES CO., LTD
Meishan, Sichuan
CN
|
Family ID: |
62978785 |
Appl. No.: |
16/341875 |
Filed: |
January 10, 2018 |
PCT Filed: |
January 10, 2018 |
PCT NO: |
PCT/CN2018/072034 |
371 Date: |
April 12, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07D 219/02 20130101;
C07D 487/08 20130101; H01L 51/0057 20130101; C09K 11/06 20130101;
H01L 51/0051 20130101; H01L 51/0071 20130101; H01L 51/0052
20130101; H01L 51/0073 20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C07D 219/02 20060101 C07D219/02; C07D 487/08 20060101
C07D487/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2017 |
DE |
10 2017 101 432.2 |
May 11, 2017 |
EP |
17170682.3 |
Claims
1. An optoelectronic device in which upon excitation of an organic
molecule direct and fast relaxation and intersystem crossing
processes for filling the charge transfer singlet state (.sup.1CT)
from the substantially isoenergetic charge transfer triplet state
(.sup.1CT) of the organic molecule, so that a
.sup.1CT.fwdarw.S.sub.0 fluorescence occurs, without the need for
thermal activation, where S.sub.0 stands for the electronic ground
state.
2. An optoelectronic device of claim 1, wherein the direct rapid
occupation of the CT singlet state, compared to molecules which
show thermally activated delayed fluorescence (TADF), in addition,
results in 5 to 10 time faster emission decay from this CT-singlet
state.
3. An optoelectronic device of claim 1 or 2, wherein the emission
decay time of the organic molecule is less than 2 microseconds,
particularly less than 1 microseconds or less than 500 ns.
4. An opto-electronic device of claims 1 to 3, wherein the emission
is not a TADF emission.
5. An optoelectronic device of claims 1 to 4, wherein the
.sup.1CT-fluorescence with a substantially iso-energetic charge
transfer triplet (.sup.3CT) equilibrated state fluorescence from
the .sup.1CT is singlet.
6. An optoelectronic device of claims 1 to 5, wherein the organic
molecule has a structure of formula Ia or Ib, or of a structure
according to formula Ia or Ib. ##STR00025## With an aromatic or
hetero-aromatic donor segment D, D1, D2 and a two or four
non-conjugated bridges B1, B2, B3 and B4 bound aromatic or
hetero-aromatic acceptor segment A, wherein the aromatic or
hetero-aromatic moieties (donor or acceptor) are substituted with
electron-donating or -withdrawing substituents, wherein the bridges
B1, B2, B3, B4 are chosen such that they prevent pronounced
overlaps donor-HOMO to the LUMO acceptor.
7. Opto-electronic device of claim 6, wherein the organic molecule
has a structure to one of the following displayed formulas or
consists of such a structure ##STR00026## Wherein the
2,3:6,7-dibenzosuberane backbone is substituted so the electronic
properties of the aromatic ring systems are modified. The R1 to R4
are substituted with the donor D, or the R1 to R4 and R1' to R4' be
substituted by donor D1 and D2, described by the formulas Ia and
Ib. And R5 through R8 moiety is substituted with the acceptor A,
wherein Q1 to Q6 on the bridges B1 of 2,3:6,7-Dibenzosuberans was
substituted with methylene and ethylene groups. B2 of the formula
Ia and Q1 to Q6 and Q1' to Q6' of the 2,3:6,7-dibenzosuberane are
substituted by the methylene and ethylene groups, Which represent
the bridges B1 or B2 and B3 or B4 of the formulas Ib, with Bridges
Q1, Q2, and Q1' Q2' are independently selected from the group
consisting of alkyl, alkenyl, alkynyl, cycloalkyl and aryl; Q3 to
Q6 and Q3' to Q6' are independently selected from the group
consisting of H, alkyl, alkenyl, alkynyl, cycloalkyl and aryl;
where: Alkyl is a straight-chain (unbranched) or branched
(C.sub.1-C.sub.10) alkyl having 1 to 10 carbon atoms in the main
hydrocarbon chain, Alkenyl is a straight or branched
(C.sub.1-C.sub.10) alkenyl having 1 to 10 carbon atoms in the main
hydrocarbon chain, Alkynyl is a straight or branched
(C.sub.1-C.sub.10) alkynyl, having 1 to 10 carbon atoms in the main
hydrocarbon chain, Cycloalkyl is a (C.sub.3-C.sub.7) -cycloalkyl
having 3 to 7 ring carbon atoms, and Aryl is a 5-ring or 6-membered
aromatic or heteroaromatic group, "main hydrocarbon chain" used
herein is the longest chain of the branched or non-linear alkyl,
alkenyl or alkynyl; Wherein Each group Q1 to Q6 and Q1' to Q6'
independently may be substituted or unsubstituted with one or more
F, Cl, Br, alkoxyl, thioalkoxyl, amine, silane, phosphine, borane,
or aryl; the groups Q1 and Q2, Q3 and Q4 groups, the groups Q5 and
Q6, the groups Q1' and Q2', the groups Q3' and Q4', as well as the
groups Q5' Q6' and are optionally chemically linked together to
form other ring systems. Donor member: R1 to R4 and R1' to R4' are
independently selected from the group consisting of H, alkyl,
alkenyl, alkynyl, cycloalkyl, alkoxyl, thioalkoxyl, amine,
phosphine, silane, borane, fluorine, chlorine, bromine. Below at
least one position of R1 to R4 in the formulas IIb and Akr to IIe
is at least one position of R1 to R4 Akr and at least one position
of R1' to R4' Akr with reference to formula III defined group Akr
wherein, in formula IIa. Wherein: Alkyl is a straight or branched
C.sub.1-C.sub.10) alkyl having 1 to 10 carbon atoms in the main
hydrocarbon chain, Alkenyl is a straight or branched
C.sub.1-C.sub.10) alkenyl having 1 to 10 carbon atoms in the main
hydrocarbon chain, Alkynyl is a straight or branched
C.sub.1-C.sub.10) alkynyl, having 1 to 10 carbon atoms in the main
hydrocarbon chain, Cycloalkyl is a (C.sub.3-C.sub.7)-cycloalkyl
having 3 to 7 ring carbon atoms, and Aryl is a 5-ring or 6-ring
aromatic or heteroaromatic group, wherein the substitutions
alkoxyl, thioalkoxyl, amine, phosphine, silane and borane is in
each case an alkoxyl OR', SR' thioalkoxyl, amine NR'R'', phosphine
PR'R'', silane SiR'R''R''' and borane BR'R''. Wherein R', R'' and
R''' independently a straight or branched C.sub.1-C.sub.10) alkyl,
(C.sub.1-C.sub.10)-alkene, (C.sub.1C.sub.10) alkyne,
(C.sub.3-C.sub.7) cycloalkyl or a 5-ring or 6-ring which aromatic
or heteroaromatic group; wherein the group Akr has a structure of
the formula IIIa and IIIb or consists of Formula IIIa Formula IIIb
##STR00027## Wherein: # marks the point through which the Akr group
is connected to the rest of the molecule, R9 to R16 and R9' to R16'
are independently selected from H, (C.sub.1-C.sub.10) alkyl,
(C.sub.1-C.sub.10)-alkenyl, (C.sub.1-C.sub.10)-alkynyl,
(C.sub.3-C.sub.7) cycloalkyl, alkoxyl oR; amine NR'R'', phosphine
PR'R'', silane SiR'R''R''', borane BR'R'', fluorine, chlorine,
bromine, or aryl, wherein the R', R'' and R''' is a straight or
branched (C.sub.1-C.sub.10) alkyl, (C.sub.1-C.sub.10) alkene,
(C.sub.1-C.sub.10) alkyne, (C.sub.3-C.sub.7) cycloalkyl or a 5
mean-Ring- or 6-membered aromatic or heteroaromatic group; Q7, Q8,
and Q7' Q8' are defined as Q1 to Q6 and Q1' to Q6' and may be
linked together to form a further ring system; Acceptor: R5 to R8
are independently selected from H, CH.sub.3, CN, COR', CO (OR'), CO
(NR'R''), SO.sub.2R; SO.sub.2 (OR'), SOR', CF.sub.3, CF.sub.2R',
wherein R' and R'' are straight or branched (C1-C10) alkyl,
(C.sub.1-C.sub.10) alkene, (C.sub.1-C.sub.10) alkyne,
(C.sub.3-C.sub.7) cycloalkyl or a 5-membered ring- or 6-membered
aromatic or heteroaromatic group, and at least one group is not H
or CH.sub.3; wherein in the formula IIa, at least two substituents
selected from R5, R6, R7 and R8 are not H or CH.sub.3; This would
mean that R5 to R8 right akr can be actually required and optional
two adjacent groups selected from R5, R6, R7 and R8 are linked with
each other chemically
8. An opto-electronic device of claim 7, wherein the organic
molecule has or consists of a structure according to the formulas
IVa to IVd ##STR00028## ##STR00029## wherein the substituents R1 to
R8, R1' to R8', Q3 are explained by Q6 and Q3' to Q6' from the
formulas IIa to IIe and the substituents R9 to R16 and Q7 to Q8
from the formulas IIIa and IIIb, wherein R16 to R23 and R16' are
defined by R23' as while as R9 to R16 and R9' to R16'.
9. An opto-electronic device of claim 7, wherein the organic
molecule has or consists of a structure according to formula V;
##STR00030## wherein the substituents R1 to R23 and Q3 to Q8 are
described under the formulas IIa to IIe, III, IIIb and IVa to IVd
and Q9 and Q10 are defined as Q1 to Q8 and Q1' to Q8' and are
optionally linked to one another so that a further ring system is
formed
10. An optoelectronic device of claim 7, wherein the organic
molecule has or consists of a structure according to formula VI
##STR00031## wherein the substituents R1 to R23, R1' to R23', Q3 to
Q10 and Q3' to Q8' are explained under the formulas IIa to IIe,
III, IIIb, IVa to IVd and V, and wherein Q9' and Q10' are defined
as Q1 to Q10 and Q1' to Q8' and are optionally linked to one
another to further form a ring system.
11. An optoelectronic device of claim 7, wherein the organic
molecule has or consists of a structure according to the formulas
VII to XVI ##STR00032## ##STR00033## ##STR00034## wherein the
substituents are as defined above
12. Optoelectronic device of claim 6, wherein the hydrogen atoms in
one, several or in all positions of the organic molecule are
replaced by deuterium
13. An organic molecule comprising a structure or consisting of a
structure according to a formula selected from the group consisting
of formula Ia, formula Ib, formula IIa, formula IIb, formula IIc,
formula IId, formula IIe, formula IIIa, formula IIIb, Formula VIII,
Formula VIII, Formula IVa, Formula IVa, Formula IVa, Formula IVa,
Formula V, Formula VI, Formula VII, Formula VIII, Formula IX,
Formula X, Formula XI, Formula XII Formula XIII Formula XIV Formula
XV and Formula XVI. The hydrogen atoms in one, several or in all
positions of the organic molecule of the abovementioned formulas
are replaced by deuterium.
14. Use of an organic molecule of claim 13 for the emission of
light, in particular in an emitter layer of an optoelectronic
device.
15. A process for preparing an optoelectronic device, wherein an
organic molecule of claim 13 is used.
16. Optoelectronic device of claims 1 to 12, organic molecule of
claim 13, use according to claim 14, method of claim 15, wherein
the optoelectronic device is selected from the group consisting of
organic light emitting diodes (OLEDs), light emitting
electrochemical cells (LEECs or LECs), OLED sensors, in particular
non-hermetically shielded gas and vapor sensors, optical
temperature sensors, organic Solar cells (OSCs), organic field
effect transistors, organic lasers, organic diodes, organic
photodiodes and "down conversion" systems
Description
SUMMARY
[0001] The invention relates to organic molecules and their use in
opto-electronic devices. These organic molecules have a donor and
acceptor moiety linked by two organic non-conjugated bridges. The
bridges show a reduced hyperconjugation. Thus singlet-triplet
energy gap of only a few meV can be achieved. This allows 100%
exciton usage in OLEDs with a short emission decay time. This new
mechanism represents direct singlet harvesting, which is
particularly suitable for use in opto-electronic devices. In
contrast to the already known according to the state of the art,
which is caused by a greater energy gap .DELTA.E
(.sup.1CT-.sup.3CT) in the order of several 100 cm.sup.'1 (some 10
meV), singlet harvesting effect with a strongly
temperature-dependent thermally activated delayed fluorescence
(TADF) takes place in direct singlet-harvesting effect with the
intersystem crossing between nearly iso-energetic .sup.3CT and
.sup.1CT states with .DELTA.E (.sup.1CT-.sup.3CT) values in the
order of 10 cm.sup.-1 (0.12 meV). In these molecules, the processes
of occupation of .sup.1CT state proceed quickly so that the
emission decay from this .sup.1CT states is in particular five to
ten times faster than the molecules that exhibit TADF.
BACKGROUND
[0002] For luminescent molecules (emitter molecules) in
optoelectronic applications, their emission decay time are required
to be as short as possible, besides, they should also have a high
emission quantum yield .PHI..sub.PL. Short emission decay times are
important, for example, to achieve long OLED device life, which
decreases the probability for chemical reactions (decompositions)
of the emitter molecules in the excited state. Moreover, for such
applications with purely organic emitter molecules, which are not
metal-complex compounds, it is important to include the electronic
occupation of the lowest excited triplet state T.sub.1 in the
emission process. This requirement can be satisfied by setting a
sufficiently small energy gap .DELTA.E (S.sub.1-T.sub.1) between
the T.sub.1 state and the overlying singlet state S.sub.1, to allow
a thermally activated delayed fluorescence (TADF) at room
temperature (FIG. 1). This process is known to person skilled in
the art (see, for example, B C A Parker, C G Hatchard, Trans.
Faraday, Royal Society of Chem., 1961, 57, 1894) and is also
referred to as E-type up conversion, first discovered for Eosin. As
a result, an effective TADF is achievable that the decay time of
the luminescence (emission) .tau. (TADF) is reduced by several
orders of magnitude, compared with that of the phosphorescence
.tau. (T.sub.1) with the involvement of long-lived triplet state.
Furthermore, in many cases, it can be achieved that the emission
quantum yield .PHI..sub.PL is increased significantly, because the
non-radiative processes from the T.sub.1 state (shown in FIG. 1)
are less important, compared with the competing faster return cast
process T.sub.1.fwdarw.k.sub.BT.fwdarw.S.sub.1.
[0003] It is known from the prior report that many molecules with
intramolecular charge transfer (CT) transition between a donor (D)
and an acceptor (A) segment may show TADF property. However, the
energy gap .DELTA.E (S.sub.1-T.sub.1) is still too large, and thus
the photophysical properties required for many applications, such
as a short decay without long decay foothills are not
achievable.
DESCRIPTION
[0004] Surprisingly, it has now been able to find a method
(molecular structural principle) which allows to reduce the energy
gap .DELTA.E (S.sub.1-T.sub.1) selectively to provide corresponding
pure organic molecules. This energy gap is approximately
proportional to the quantum mechanical exchange integral according
to equation (1)
.DELTA.E(S.sub.1-T.sub.1).apprxeq.const.<.psi..sub.D(r.sub.1).psi..su-
b.A*(r.sub.2)|r.sub.12.sup.-1|.psi..sub.D(r.sub.2).psi..sub.A*(r.sub.1)>-
; (1)
[0005] Herein, r.sub.1 and r.sub.2 are the electron coordinates;
r.sub.12 is the distance between the electron 1 and electron 2;
.psi..sub.D is the wave function of the HOMO (highest occupied
molecular orbital), extending mainly over the donor segment of the
molecule; .psi..sub.A* is the wave function of the LUMO (lowest
unoccupied molecular orbital), extending primarily over the
acceptor part of the molecule. Based on the equation (1) it is
apparent that .DELTA.E (S.sub.1-T.sub.1) is small when the product
of the wave functions [.psi..sub.D(r.sub.1).psi..sub.A*(r.sub.2)]
is small. This requirement can not be reached for a variety of
molecules with intramolecular CT transitions because spatial
extension of the wave functions .psi..sub.D(r.sub.1) and
.psi..sub.A*(r.sub.2) overlaps, resulting in large .DELTA.E
(S.sub.1-T.sub.1) values. According to the invention, molecular
structures are proposed which markedly reduced superposition of the
wave functions. This is achieved by molecular structures in which
the donor or acceptor moieties are separated by non-conjugated
small chemical groups (bridges). As a result, the extension of the
HOMO into the acceptor region and the LUMO into the donor region
are greatly reduced. Moreover, by chemical reinforcement of one or
both bridges, it is possible to reduce the flexibility of the donor
and the acceptor part. This makes it possible to increase the
emission quantum yield and to reduce the .DELTA.E (S.sub.1-T.sub.1)
values and inhomogeneity of the emitter molecules.
[0006] In the molecules of the invention with extremely reduced
overlaps of the wave functions, the hyperconjugations presented in
the non-conjugated small chemical groups (bridges) (known to a
person skilled in the art) are reduced by substitutions. This
further reduces the extent of the HOMO into the acceptor region and
the LUMO into the donor region.
[0007] The molecules of the invention are usually present in
optoelectronic devices with other molecules, eg., evaporated with
other small molecules or doped in polymers. These are referred to
herein as matrices or matrix materials. The molecules of the
invention can also be dissolved, and the solvent is then being the
matrix. The energy levels of the molecules of the invention, which
are incorporated or dissolved in such matrix
materials/environments, doped or dissolved, are influenced in
different ways by the polarity of the matrix. This property is
explained further below.
[0008] Formulas Ia and Ib show the structure motif of the organic
molecules of the invention with two organic bridges between the
donor and acceptor segments. By suitable selection of these
bridges, the spatial overlap of HOMO (predominantly lying on the
donor) and LUMO (predominantly on the acceptor) can be
significantly reduced, by largely suppressing the hyperconjugation
by substitution (s) in one or both bridges. A remaining slight
overlap of orbitals is, however, useful in order not to make the
transition probability between the electronic ground state S.sub.0
and the excited S.sub.1 state (.sup.1CT-state) be too small [R.
Czerwieniec et al., Coord. Chem. Rev. 2016, 325, 2-26]. In
addition, the two-bridges lead to stiffening of the molecule. This
results in an increase in the emission quantum yield as well as a
reduction in the emission half-value range. In many cases, the
latter is useful to achieve a desired emission color (color purity)
for the light generation in OLEDs. Furthermore, the occurrence of
the long-lived tails of the emission decay curves is largely
suppressed.
[0009] The Formulas Ia and Ib show structural motifs of the organic
molecules of the invention consisting of an aromatic or a
heteroaromatic donor segment D, D1, D2 and an aromatic or a
heteroatom which is bonded via two or four non-conjugated bridges
B1, B2, B3 and B4, and aromatic acceptor segment A. The aromatic or
heteroaromatic moieties are substituted with electron-withdrawing
substituents and thereby become donors and acceptors, respectively.
Exemplary embodiments are given below. The bridges are selected in
such a way that they prevent pronounced overlaps of the donor HOMO
with the acceptor LUMO. The bridge B2 and/or the bridge B3 can, for
example, have an aromatic or heteroaromatic unit. In particular,
the bridges have a reduced hyperconjugation compared to the prior
art. This results in a substantially smaller energy difference
.DELTA.E (.sup.1CT-.sup.3CT), as will be explained further
below.
##STR00001##
[0010] For optoelectronic applications with a request of a small
.DELTA.E (S.sub.1-T.sub.1) value, it is important that the energy
gap between the HOMO localized on the donor and the acceptor
localized on the LUMO is in the range between 1.8 and 3.3 eV, thus
allow the energy of the HOMO.fwdarw.LUMO transition to be in the
visible region. The energy levels of HOMO and LUMO can be described
by the strengths of the electron-donating (for the donors) or the
electron-withdrawing (for the acceptors) effects. These terms are
known to a person skilled in the art and are also described below
in concrete embodiments.
[0011] In the invention, the energy gap .DELTA.E (S.sub.1-T.sub.1)
of molecules is less than 20 cm.sup.-1 (2.5 meV), more preferably
less than 10 cm.sup.-1 (.apprxeq.1.2 meV). Thus, the singlet and
triplet states of charge transfer in comparison to the present at
room temperature the thermal energy k.sub.BT=210 cm.sup.-1 are
substantially isoenergetic. Detailed instructions on the molecular
structure are given below. The corresponding value is determined by
the individual molecule. It can be determined by quantum mechanical
calculations, for example, using TD-DFT programs (eg. with the
Gaussian 09 program, especially when using an MO6 functional) or
the freely available NWChem version (eg Version 6.1), the CC2
method (TURBOMOLE GmbH, Karlsruhe) or a CAS method (Complete
ActiveState method). [See, e.g., B D I Lyakh, M. Musiaz, V F
Lotrich, R J Bartlett, Chem. Rev. 2012, 112, 182-243 and P G
Szalay, T. Muller, G. Gidofalvi, H. Lischka, R. Shepard, Chem. Rev.
2012, 112, 108-181]. Exemplary embodiments are given below.
[0012] The emission decay time .tau. (300 K) should be less than 2
microseconds, better less than 1 microseconds for practical
applications,. To achieve this, in addition to the adjustment of a
small .DELTA.E (S.sub.1-T.sub.1) value, it may be useful to tune
the spin-orbit interaction (SBK, SOC) between the T.sub.1 state and
higher molecular energy states, in order to obtain a larger
intersystem crossing (ISC) rate. For this purpose, for example, a
substitution of the donor segment D and/or the acceptor segment A
and/or one or both bridges with a halogen Cl, Br and/or I is
suitable.
[0013] An increase in the rate of ISC for the inventive molecules
is also achieved by the CT states energetically closely spaced to
the donor D and/or acceptor A and/or one or both bridges lying
localized triplet states .sup.3LE (LE=excited localized). The
increase in ISC rate between .sup.1CT and .sup.3CT states is given
by a reinforcement of the spin-orbit interaction due to quantum
mechanical mixtures between these states and the .sup.3LE states.
The target molecules are determined by using known computer
programs or quantum mechanical methods (eg Gaussian 09 or CC2
method). These mixtures more effective and the closer states are
energetically adjacent. A mutual energetic shift can be achieved by
means of changes in the donor and/or acceptor strengths as well as
changes in electron-donating substitutions on the donor and/or
changes in electron-accepting substitutions at the acceptor. Also,
by using more than one electron-pushing and/or pulling
substitutions, an energetic shift can be achieved. Importantly, in
one embodiment of the invention, a matrix with suitable polarity
can be used. As a result, the blank, .sup.1CT and .sup.3CT states,
in contrast to .sup.3LE states move energetically (if the organic
molecule does not have the desired sequence of states), so that the
.sup.1,3CT-states are below or lie only slightly above the
.sup.3LE-conditions. The polarity of the matrix can be described by
the dielectric constant .epsilon.. (Values can be found in the
respective literature tables). The influence of the polarity can
also be detected by the above mentioned calculation programs.
[0014] The influence of the polarity of the matrix, for example,
the solvent, will be explained with reference to FIG. 2. In this
Figure, the red shift of the emission spectra is shown with
increasing polarity of the solvent (quantified by the dielectric
constant .epsilon.. The emission results from a molecule of the
invention is described below (example molecule 1).
[0015] The organic molecules of the invention are constructed in
such a way that .sup.1CT and .sup.3CT-conditions are below the
.sup.3LE states, for example, less than 1500 cm.sup.-(.apprxeq.190
meV), preferably less 500 cm.sup.-1 (.apprxeq.63 meV) or more
preferably less than 100 cm.sup.-1 (.apprxeq.12 meV). An energetic
position of the .sup.3LE-conditions slightly below the .sup.1CT and
.sup.3CT-conditions (eg., 50 cm.sup.-1.apprxeq.6 meV) is also
possible. The corresponding energy gaps can be determined by
quantum-theoretical TD-DFT calculations. Moreover, it can be
experimentally determined whether the localized .sup.3 LE state is
energetically below the .sup.1.3CT-states by recording
low-temperature emission spectra (eg. at 77 K or 10 K). In this
case, the emission is structured so that vibration satellites can
be resolved. In addition, the emission decay time of the emitting
.sup.3LE state, which is in the range of ms to s, is significantly
longer than the .sup.1CT-decay time (<2 microseconds). In the
opposite case, broad CT spectra is found with half-widths of
several thousand cm.sup.-1 and short decay time.
[0016] The chemical bonding between the donor and acceptor segments
of the organic molecule not only have the effect of stiffening of
the molecule, but also surprisingly lead to an increase of the
emission quantum yield .PHI..sub.PL.
[0017] In addition, the bridges cause a strong restriction on the
free mobility of the donor molecule segment D and the acceptor
molecule segment A of the organic molecule. The long-term emission
decay time often encountered in the prior art, are significantly
reduced in the region of the long-lived "decay tails". An
improvement in the color purity of the emission is also achieved by
reducing the half-width of the emission band.
[0018] Surprisingly, the molecules of the invention (optionally
together with a matrix having a polarity, described by the
dielectric constant in the range of
2.4.ltoreq..epsilon..ltoreq.5.0), which show the effective ISC and
a very small energy gap .DELTA.E (.sup.1CT-.sup.3CT) less than 20
cm.sup.-1 (2.5 meV), preferably less than 10 cm.sup.-1
(.apprxeq.1.2 meV), only give a .sup.1CT-fluorescence, without a
time delayed TADF emission. With a value of less than 2 .mu.s to
less than 500 ns, this is clearly more short-lived than that of the
prior art TADF emitters. The organic molecules of the invention,
possibly together with a matrix as a composition or combination,
which are used as emitters in OLEDs, can collect all the singlet
and triplet excitons in the singlet charge-transfer state, in a
time window which is within the decay time of the fluorescence. It
is a "Direct Singlet Harvesting Effect". As a result, the
emitter-matrix combinations of the invention show only the short
decay times of the fluorescence, and the energy gap is only a few
hundred ns to 1 or 2 .mu.s. This fluorescence is equilibrated with
the nearly iso-energetic .sup.3 CT-state fluorescence from the
.sup.1CT-singlet state. In contrast to the known singlet harvesting
effect with a strongly temperature dependent thermally activated
delayed fluorescence (TADF) (caused by a greater energy difference
.DELTA.E (.sup.1CT-.sup.3CT) in the range of some 10.sup.2
cm.sup.-1), "Direct Singlet Harvesting Effect" takes place between
the ISC nearly iso-energetic .sup.3CT and .sup.1CT states. In these
molecules, optionally in combination with a matrix, the processes
fill the .sup.1CT-state quickly so that the emission decay from
these .sup.1CT states in particular is five to ten times shorter
than TADF molecules.
Description of the Molecular Structure of Formulas Ia and Ib
[0019] According to the formulas Ia and Ib, the molecular structure
of the emitter materials in the invention is explained further by
means of the formulas IIa to IIe. The concomitant use of polar
matrices, with a dielectric constant (polarity) of
2.4.ltoreq..epsilon..ltoreq.4.5 in a composition comprising an
organic molecule of the invention, can lead to further improvements
in the direct singlet-harvesting effect (reduction of the
.sup.1CT-fluorescence decay time).
##STR00002##
[0020] According to the formulas IIa to IIe, the basic skeleton of
the organic molecules in the invention is 2,3:6,7-dibenzosuberan.
By means of suitable substitutions shown here, the electronic
properties of the aromatic ring systems are controlled. The
molecule part substituted by R1 to R4 is the donor part D or the
molecule parts substituted by R1 to R4 and R1' to R4' become donor
parts D1 and D2 in the sense of the formulas Ia and Ib and the one
with R5 to R8 or the molecule part substituted with R5 and R6
becomes the acceptor part A. The methylene and ethylene groups of
the 2,3:6,7-dibenzosuberane, which are substituted by Q1 to Q6,
represent the bridges B1 and B2, respectively, and the methylene
and ethylene groups substituted by and Q1' to Q6' of the
2,3:6,7-dibenzosuberans represent the bridges B3 and B4 of the
formulas Ia and Ib.
[0021] Bridges:
[0022] Q1, Q2, Q1' and Q2' are each independently selected from
alkyl, alkenyl, alkynyl, cycloalkyl or aryl.
[0023] Q3 to Q6 and Q3' to Q6' are each independently selected from
H, alkyl, alkenyl, alkynyl, cycloalkyl or aryl.
[0024] wherein:
[0025] Alkyl is a straight-chain (unbranched) or branched
(C.sub.1-C.sub.10) alkyl having 1 to 10 carbon atoms in the main
hydrocarbon chain (eg. Methyl, ethyl, n-propyl, i-propyl, n-butyl,
i-Butyl, t-butyl, n-pentyl, etc.),
[0026] Alkenyl is a straight or branched (C.sub.1-C.sub.10) alkenyl
having 1 to 10 carbon atoms in the main hydrocarbon chain (eg.
propen-2-yl, n-buten-2-yl, n-buten-3-yl),
[0027] Alkynyl is a straight or branched (C.sub.1-C.sub.10)
alkynyl, having 1 to 10 carbon atoms in the main hydrocarbon chain
(eg. propen-2-yl, n-buten-2-yl, n-buten-3-yl),
[0028] Cycloalkyl is a (C.sub.1-C.sub.10)-cycloalkyl having 3 to 7
ring carbon atoms, and
[0029] Aryl is a 5-membered or 6-membered aromatic or
heteroaromatic group, benzene, thiophene, furan, imidazole, azole,
diazole, triazole, tetrazole, oxazole, etc.
[0030] "Main hydrocarbon chain" means the longest chain of the
branched or non-straight-chain alkyl, alkenyl or alkynyl.
[0031] Each group of Q1 to Q6 and Q1' to Q6' can be substituted or
unsubstituted by one or more F, Cl, Br, alkoxy, thioalkoxyl, amine,
silane, phosphane, borane or aryl.
[0032] The groups Q1 and Q2, the groups Q3 and Q4, the groups Q5
and Q6, the groups Q1' and Q2', the groups Q3' and Q4', as well as
the groups Q5' and Q6', may be chemically linked to each other, to
further form ring systems.
[0033] Donors:
[0034] R1-R4 and R1' to R4' are each independent selected from H,
alkyl, alkenyl, alkynyl, cycloalkyl, alkoxyl, thioalkoxyl, amine,
phosphane, silane, borane, fluorine, chlorine, bromine or the group
Akr defined below by formula III. In formula IIa, at least a
position from R1 to R4 is Akr and in the formulas IIb to IIe at
least a position from R1 to R4 and at least one position from R1'
to R4' is Akr.
[0035] wherein:
[0036] Alkyl is a straight or branched (C.sub.1-C.sub.10) alkyl
(eg. Methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl,
n-pentyl, etc.) , which has 1 to 10 carbon atoms in the main
hydrocarbon chain,
[0037] Alkenyl is a straight or branched (C.sub.1-C.sub.10) alkenyl
(eg. propen-2-yl, n-buten-2-yl, n-buten-3-yl) containing 1 to 10
carbon atoms in the main hydrocarbon chain having,
[0038] Alkynyl is a straight or branched (C.sub.1-C.sub.10) alkynyl
(eg. propen-2-yl, n-buten-2-yl, n-buten-3-yl) containing 1 to 10
carbon atoms in the main hydrocarbon chain having,
[0039] Cycloalkyl is a (C.sub.3-C.sub.7) -cycloalkyl having 3 to 7
ring carbon atoms, and
[0040] Aryl is a 5-membered or 6-membered aromatic or
heteroaromatic group, benzene, thiophene, furan, imidazole, azole,
diazole, triazole, tetrazole, oxazole, etc.
[0041] The alkoxyl, thioalkoxyl, amine, phosphane, silane and
borane substitutions are each an alkoxyl OR', thioalkoxyl SR',
amine NR'R'', phosphane PR'R'', silane SiR'R''R''' and borane
BR'R'', where R', R'' and R''' are each independent selected from a
straight or branched (C.sub.1-C.sub.10) alkyl, (C.sub.1-C.sub.10)
alkene, (C.sub.1-C.sub.10) alkyne, (C.sub.3-C.sub.7) cycloalkyl or
a 5-ring or 6-membered aromatic or heteroaromatic group mean.
[0042] The group Akr consists of a structure of the formulas IIIa
and IIIb:
##STR00003##
[0043] wherein:
[0044] # marks the site through which the Akr group is attached to
the rest of the molecule,
[0045] R9 to R16 and R9' to R16' are independently selected from H,
(C.sub.1-C.sub.10)-alkyl, (C.sub.1-C.sub.10)-alkenyl,
(C.sub.1-C.sub.10)-alkynyl, (C.sub.3-C.sub.7)-Cycloalkyl, alkoxyl
OR', amine NR'R'', phosphane PR'R'', silane SiR'R''R''', borane
BR'R'', fluorine, chlorine, bromine or aryl, where radicals R', R''
and R''' is independently straight or branched (C.sub.1-C.sub.10)-
alkyl, (C.sub.1-C.sub.10)-alkene, (C.sub.1-C.sub.10)-alkyne,
(C.sub.1-C.sub.10)-cycloalkyl or a 5-ring or 6-membered aromatic or
heteroaromatic group;
[0046] Q7, Q8, Q7' and Q8' are defined as Q1 to Q6 and Q1' to Q6'
and may be linked to each other or further form a ring system.
[0047] Acceptor:
[0048] R5 to R8 are independently H, CH.sub.3, CN, COR', CO (OR'),
CO (NR'R''), SO.sub.2R', SO.sub.2(OR'), SOR', CF.sub.3, CF.sub.2R',
in which R' is as defined above. At least one group is not H or
CH.sub.3.
[0049] Furthermore, at least two substituents selected from R5, R6,
R7 and R8 are not H or CH.sub.3 in the formula IIa, preferably.
[0050] In one embodiment of the molecules of the invention, two
adjacent groups selected from R5, R6, R7 and R8 may be chemically
linked to each other. Such linkages, which results in a stiffening
effect of the molecular structure, as well known to a person
skilled in the art, can lead to an increase in the emission quantum
yield.
[0051] In one embodiment of the molecules according to the
invention, hydrogen atoms can be replaced by deuterium at one,
several or all positions in the molecule of the formula IIa to IIe
according to the invention, in order to increase the emission
quantum yield.
[0052] In a further embodiment, the molecule has a structure of
Formulas IVa to IVd according to the invention.
##STR00004## ##STR00005##
[0053] The substituents R1 to R8, R1' to R8', Q3 to Q6 and Q3' to
Q6' are described under the Formulas IIa to IIe and the
substituents R9 to R16 and Q7 to Q8 are described under the
Formulas IIIa and IIIb. R16 to R23 and R16' to R23' are defined as
R9 to R16 and R9'to R16'.
[0054] In a further preferred embodiment, the organic molecule has
a structure of Formula V according to the invention.
##STR00006##
[0055] The substituents R1 to R23 and Q3 to Q8 are explained under
the formulas IIa to IIe, III, IIIb and IVa to IVd.
[0056] Q9 and Q10 are defined as Q1 to Q8 and Q1' to Q8' and may be
linked to each other, so that a ring system is further formed.
[0057] In a further preferred embodiment, the organic molecule has
a structure of formula VI according to the invention.
##STR00007##
[0058] The substituents R1 to R23, R1' to R23', Q3 to Q10 and Q3'
to Q8' are explained under the formulas IIa to IIe, III, IIIb, IVa
to IVd and V.
[0059] Q9' and Q10' are defined as Q1 to Q10 and Q1' to Q8' and may
be linked to one another, so that a ring system is further
formed.
[0060] In further preferred embodiments, the organic molecule has
structures of the Formulas VII to XVI according to the
invention.
##STR00008## ##STR00009## ##STR00010##
[0061] The above mentioned definitions apply.
EXAMPLES
[0062] The organic molecules presented in the invention, which may
be part of a composition or combination with a matrix material, can
be synthesized through known catalytic coupling reactions (eg,
Suzuki coupling reaction, Buchwald-Hartwig cross-coupling
reaction).
[0063] The organic molecules (emitter molecules) have an energy gap
between the charge-transfer conditions .DELTA.E
(.sup.1CT-.sup.3CT), which is less than 20 cm.sup.-1 (2.5 meV),
preferably less than 10 cm.sup.-1 (.apprxeq.1.2 meV). In contrast
to the previous technology, this small difference in energy is
achieved by an bridge(s), in which existing Hyper-Conjugation is
significantly reduced by substitution(s) at the C.sub.1-bridge B2
and B3. The structure motif is illustrated here:
##STR00011##
[0064] in which
[0065] # marks the position in which the carbon atom or the spiro
carbon atom of the bridge B2 or B3 is connected to the donor or
acceptor fragment in the molecule of the formula Ia or Ib.
Furthermore: Q1, Q2, Q1' and Q2' .noteq.H.
[0066] The emitter molecules are in a solid matrix (e.g. in OLEDs)
and thus represent the emission layer. The polarity of the matrix
is selected so that the localized .sup.3LE states are energetically
above the .sup.1,3CT states, for example, less than 1500 cm.sup.-1
(.apprxeq.190 meV) or preferably less 500 cm.sup.-1 (.apprxeq.63
meV), more preferably less than 100 cm.sup.-1 (.apprxeq.12 meV). On
the other hand, the .sup.3LE state may be 50 cm.sup.-1 (.apprxeq.6
meV) below the .sup.13CT states. The matrix polarity can be
selected, for example, in terms of the dielectric constant
.epsilon., in the range of 2.2.ltoreq..epsilon..ltoreq.5.0.
Example 1
##STR00012##
[0067] Example Molecule 1
[0068] Hereinafter, the molecule shown in example 1 according to
the invention is discussed in more detail.
[0069] The frontier orbitals shown in FIG. 3 show that HOMO and
LUMO are located in distinctly different regions of the molecule.
This suggests that the energy splitting between the lowest triplet
and the above singlet state is small. Calculation for the example
molecule 1 in a TD-DFT calculation (Functional B3LYP and also
Functional MO6) shows that the energy difference for the optimized
triplet geometry .DELTA.E (.sup.1CT-.sup.3CT)=7 cm.sup.-1 (0.87
meV). Thus, example 1 represents an emitter molecule according to
the invention, which is suitable for use in optoelectronic devices,
such as OLEDs.
[0070] The chemical synthesis of the molecule example 1 started
from commercially available materials is shown in the following
scheme.
##STR00013##
[0071] Chemical Analysis:
[0072] .sup.1H NMR (300 MHz, CDCl.sub.3, .delta.): 7.71 (d, J=7.5
Hz, 2H), 7.66 (s, 1H), 7:34 (q, J=7.5 Hz, 6H), 7.22 (d, J=7.5 Hz,
1H), 7.11 (d, J=7.5 Hz, 2H), 6.92 (d, J=7.5 Hz, 1H), 6.80 (t, J=9
Hz, 3H), 6.71 (t, J=7.5 Hz, 2H), 6.32 (d, J=3 Hz, 1H), 5.72 (d,
J=7.5 Hz, 2H), 3.48 (d, J=3.6 Hz, 4H), 1.53 (s, 6H). .sup.13C NMR
(75 MHz, CDCl.sub.3, .delta.): 156.35, 148.69, 148.36, 140.53,
130.07, 129.22, 128.59, 126.07, 124.79, 124.67, 121.51, 120.43,
113.66, 66.47, 38.13, 36.73, 35.82, 30.49. MS (HR-ES-MS=high
resolution electrospray mass spectrometry) m/z:
C.sub.44H.sub.31N.sub.3 gives: 601.2518; found 601.3514.
C.sub.44H.sub.31N.sub.3 results: C, 87.82; H, 5.19; N, 6.98, found:
C, 87.48; H, 5.41; N, 6.60.
[0073] Crystal Structure:
[0074] FIG. 4 shows the molecular structure which results from an
X-ray structure determination. Further structural data are
summarized in Tables 1 and 2.
TABLE-US-00001 TABLE 1 X-ray diffraction data for the molecule of
Example 1. Formula C.sub.44H.sub.31N.sub.3 D .sub.calc/G cm .sup.-3
1.237 .mu./mm.sup.-1 0.556 Molar mass 601.72 Colour yellow Shape
irregular Size/mm .sup.3 0.21 .times. 0.20 .times. 0.14 T/K 123.00
(10) crystal system monoclinic space group P2.sub.1/c a/.ANG.
10.68690 (10) b/.ANG. 12.46700 (10) c/.ANG. 24.3981 (3) a/.degree.
90 b/.degree. 96.2130 (10) g/.degree. 90 V/.ANG. .sup.3 3231.55 (6)
Z 4 Z ' 1 Wavelength/.ANG. 1.54184 Radiation CuK .sub.a
.THETA..sub.min/.degree. 3.645 .THETA..sub.max/.degree. 73.424
Measured 35409 reflections Independent 6430 reflections Used
reflections 5714 R.sub.int 0.0284 Parameter 426 Restrictions 0 the
biggest Peak 0.229 the deepest hole -0.238 GoF 1.024 wR .sub.2 (all
data) 0.1037 wR .sub.2 0.0988 R .sub.1 (all data) 0.0438 R .sub.1
0.0388
TABLE-US-00002 TABLE 2 Atomic coordinates x, y, z (x 10 .sup.4
.ANG.) and displacement parameters U (eq) (.ANG..sup.2 .times.
10.sup.3) for the example molecule 1. C(16) 7402.8(10) 2049.8(9)
5585.6(4) 23.7(2) C(21) 8030.3(11) 3858.2(9) 3240.5(5) 24.8(2)
C(19) 7645.4(10) 3096.7(8) 4145.6(4) 21.4(2) C(22) 8573(1)
3936.8(9) 2753.4(5) 25.2(2) C(1) 6884.5(11) 2918.2(9) 6429.5(5)
24.9(2) C(5) 5332.2(11) 1756.1(9) 5912.3(5) 24.3(2) C(40)
7533.0(11) 4274.0(9) 4318.0(4) 25.7(2) N(2) 10626.8(11) 3462.3(12)
1766.7(5) 47.8(3) C(25) 9216.8(11) 2264.9(9) 3493.5(5) 26.1(2)
C(33) 6256.0(11) 2827.1(10) 3965.1(4) 25.5(2) C(30) 8434.4(11)
1387(1) 5703.9(5) 28.7(3) C(32) 8222.1(11) 4777.5(10) 2362.9(5)
30.4(3) C(23) 9493.8(11) 3196(1) 2638.9(5) 26.9(2) C(28) 9138.5(11)
1837.9(9) 4812.4(5) 25.5(2) C(29) 9292.5(12) 1309.6(10) 5322.5(5)
30.6(3) C(4) 4527.6(11) 1832.9(9) 6326.9(5) 28.0(2) C(6) 4920.9(12)
1231.6(9) 5415.4(5) 29.5(3) C(24) 9783.3(12) 2364.2(10) 3005.9(5)
29.4(3) C(39) 6273.3(12) 4601.8(10) 4262.2(5) 31.6(3) C(34)
5755.3(12) 1848.6(11) 3783.0(5) 33.3(3) C(2) 6125.4(12) 3020(1)
6861.2(5) 29.6(3) C(3) 4907.4(12) 2390.2(10) 6877.4(5) 30.8(3)
C(15) 7982.5(12) 3530.6(10) 6432.3(5) 31.8(3) C(7) 3735.3(12)
784.4(10) 5331.2(6) 35.6(3) C(38) 5484.3(12) 3714.1(11) 4032.5(5)
32.2(3) C(27) 10145.3(12) 1681.8(11) 4433.3(5) 31.4(3) C(26)
9615.5(13) 1326.1(10) 3858.0(5) 31.9(3) C(41) 8492.1(14) 4958.6(10)
4511.5(5) 34.9(3) C(31) 10125.5(11) 3318.4(11) 2151.1(5) 32.9(3)
C(9) 3345.8(12) 1353.5(11) 6230.5(6) 38.1(3) C(8) 2943.3(12)
838.5(11) 5740.3(7) 40.8(3) C(44) 5964.0(16) 5627.9(11) 4426.3(6)
43.9(4) C(11) 5092.0(14) 1528.7(12) 7334.7(6) 42.4(3) C(14)
8339.7(14) 4229.3(11) 6862.5(6) 41.2(3) C(10) 3850.2(14) 3162.4(13)
7009.6(6) 42.7(3) C(12) 6530.2(14) 3722.4(12) 7290.8(6) 41.8(3)
C(35) 4458.2(14) 1764.8(14) 3659.6(6) 46.5(4) C(42) 8171.6(17)
5992.8(11) 4664.7(6) 48.4(4) C(37) 4182.6(13) 3620.1(15) 3900.4(6)
47.3(4) C(13) 7613.4(15) 4322.9(13) 7297.2(6) 47.4(4) C(43)
6920.2(18) 6310.2(11) 4629.1(6) 52.0(4) C(36) 3693.7(14) 2642.2(17)
3713.7(6) 54.3(4)
[0075] The example molecule 1 can be vacuum-sublimed (Temperature
250.degree. C., Pressure 6.times.10.sup.-5 mbar) and can also
dissolve in many organic solvents, such as in Dichloromethane
(CH.sub.2Cl.sub.2), Toluene, Tetrahydrofuran (THF), Acetone,
Dimethylformamide (DMF), Acetonitrile, Ethanol, Methanol, Xylene or
Benzene. The good solubility in Chloroform also allows doping, for
example, in Polymethylmethacrylate (PMMA) or polystyrene.
[0076] Photophysical Measurements
[0077] Example molecule 1 dissolved in toluene with a value of
dielectric constant .epsilon.=2.4 (T=300 K) shows an emission
(T=300 K) with a maximum in blue at 468 nm (FIG. 5). The emission
quantum yield .PHI..sub.PL is high (.PHI..sub.PL=65% for a
nitrogen-purged solution). The decay time for example 1 is only 420
ns (FIG. 6). A short decay time is very important for OLED
applications, because short decay time have less roll-off effects
and increases the device stability, which is well-known to the
person skilled in the art. Emitter has a shorter decay time,
compared with the reported TADF decay time (about 5 .mu.s).
[0078] DFT calculations (FIG. 3) show the Charge-Transfer (CT)
transitions of sample molecule 1. Such transitions are influenced
by the immediate vicinity of the emitter (Matrix/Solvent). FIG. 2
illustrates this behavior. With increasing polarity of the matrix,
the emitting of .sup.1CT-singlet state has a red shift.
Corresponding statements also result from TD-DFT calculations, in
which dielectric constant .epsilon. is considered mathematically as
a parameter.
[0079] The effect of the polarity of the matrix is also
investigated with example molecule 1 dissolved in diethyl ether.
This matrix has a higher value on .epsilon.=4.3 than toluene. The
emission (T=300 K) shows a red-shifted maximum at 515 nm (FIG. 7a),
and the emission quantum yield .PHI..sub.PL is 70% in a
nitrogen-purged solution. The decay time of .tau.=960 ns is
determined (FIG. 7b). The corresponding radiative rate to
kr=.PHI..sub.PL/.tau.=7.3 10.sup.5 s.sup.-1 can be determined from
the given values. This emission is a fluorescence equilibrated with
the nearly iso-energetic .sup.3CT state. Further details are given
below. This interpretation is confirmed by quantum-mechanical
calculations. For electronic transition S.sub.0.fwdarw..sup.1CT,
the TD-DFT calculation results (for the .sup.1CT-geometry) give an
oscillator strength f=0.00115. The radiative rate for the
transition can be estimated based on the literature [N. Turro,
Modern Molecular Photochemistry, The Benjamin/Cummings Publ., Menlo
Park, Calif. 1978, page 87], using specified approximation and the
energetic position of the emission (FIG. 7a). The assessment gives
a radiative rate for the prompt fluorescence of
kr=6.5.times.10.sup.5 s.sup.-1, which is relatively close to the
experimentally determined rate, based on the simple approximation.
The alternative interpretation, in which emission process from the
triplet state is phosphorescence can be excluded for a liquid
solution emitter due to the short decay time of less than 1 .mu.s
and the high emission quantum yield. This value of the decay time
of 980 ns is also shorter than the shortest TADF decay time
measured so far. However, the described emission process is not a
TADF emission. It is, rather, fluorescence from the .sup.1CT
singlet state equilibrated with the nearly iso-energetic
.sup.3CT-state. When used in an OLED, all triplet and singlet
excitons are collected. This important feature will be discussed in
detail below.
[0080] FIG. 8 shows the emission characteristics of the sample
substance 1 doped in a polar matrix (with a formal .epsilon. value
of .apprxeq.4.4), the higher-energy .sup.1,3CT states of sample
molecule 1 and a small singlet-triplet energy gap. This matrix is a
TADF-emitter, but emission characteristics are not relevant here.
The structural formula of the matrix substance is:
##STR00014##
[0081] The emission spectrum of this emitter-matrix
combination/composition) is shown in FIG. 8. This emission decay
time of 530 ns is also fluorescence from the .sup.1CT-singlet
state, which is equilibrated with the iso-energetic
.sup.3CT-state
[0082] In FIG. 9, emission spectra of the sample molecule 1 for
various temperatures (T=300 K, 150 K and 10 K) were compared.
Except for a slight spectral shift, there are no changes over the
entire temperature range, as expected, in contrast to TADF-emitter
(freezing of TADF emissions). The radiative rate of emission does
not change significantly either. These measurement results show
that the emission mechanism remains unchanged over the entire
temperature range, expected as fluorescence from the 1CT-singlet
state equilibrated with iso-energetic .sup.3CT-state.
[0083] In FIG. 10, the emission behavior of the sample molecule 1
in a polar environment such as diethyl ether or the discussed solid
TADF matrix, is displayed with an energy level diagram. Low
temperature measurements show that the localized .sup.3LE-state
energy is above the .sup.1,3CT states.
[0084] Quantum mechanical mixtures of this .sup.3LE state via the
mechanisms of SOC (spin-orbit coupling=spin-orbit interaction) and
the configuration interaction (CI) are possible with the CT-states.
Furthermore, since the singlet and triplet CT states have similar
potential areas, the Franck-Condon factors responsible for the ISC
rate are large. (This term is known to a person skilled in the art)
Because of these properties, it is expected that rapid ISC occurs
between the .sup.1CT state and the .sup.3CT state. "Fast" means
that the ISC processes take place faster than the prompt
fluorescence in this context. In fact, even at low temperature
(e.g. T=10 K), no .sup.3CT phosphorescence was observed for
molecule 1 in the TADF matrix.
[0085] When the composition (emitter molecules in a polar matrix)
is used in an OLED, the singlet excitons occupy the CT-singlet and
triplet excitons occupy the CT-triplet state according to the
invention. Since the occupation of both CT states is in equilibrium
with the rapid ISC processes and the prompt .sup.1CT.fwdarw.S.sub.0
fluorescence is much faster than the spin-forbidden
.sup.3CT.fwdarw.S.sub.0 phosphorescence, fluorescence from the
.sup.1CT-singlet states equilibrated with the nearly iso-energetic
.sup.3CT state can be observed. This means that all excitation
processes can lead to the direct occupation and emission from the
CT singlet state. That is, there is a "direct singlet harvesting".
This invention thus provides organic emitter molecules for
optoelectronic devices, as well as a method for adapting these,
which lead to a significant shortening of the emission decay time
(eg., by a factor of five to ten) compared to the prior art.
Example 2
##STR00015##
[0086] Example Molecule 2
[0087] The frontier orbitals shown in FIG. 11 indicate that HOMO
and LUMO are located in distinctly different spatial regions of the
molecule. This suggests a very small splitting between the lowest
triplet CT and the above singlet CT state. A calculation for the
sample molecule 2 in a TD-DFT calculation (Functional B3LYP; basic
set 6-31G (d, p)) shows that this energy difference for the
optimized singlet geometry .DELTA.E (.sup.1CT-.sup.3CT)=5 cm.sup.-1
is (0.6 meV). Thus, example molecule 2 represents an organic
molecule of the invention.
[0088] The chemical synthesis of the molecule Example 2 started
from commercially available starting materials is explained in the
following scheme.
##STR00016##
Example 3
##STR00017##
[0089] Example Molecule 3
[0090] The frontier orbitals shown in FIG. 12 indicate that HOMO
and LUMO are located in distinctly different spatial regions of the
molecule. This suggests that the splitting between the lowest
triplet CT and the above singlet CT state is small. Calculation for
the sample molecule 3 in a TD-DFT calculation (Functional B3LYP;
basic set 6-31G (d, p)) shows that the energy gap .DELTA.E
(.sup.1CT-.sup.3CT) for the optimized singlet geometry is 5
cm.sup.-1 (0.6 meV). Thus, example molecule 3 represents an organic
molecule of the invention.
[0091] The chemical synthesis of the molecule example 3 started
from commercially available starting materials is explained in the
following Scheme.
##STR00018##
Example 4
##STR00019##
[0092] Example Molecule 4
[0093] Calculation for the sample molecule 4 in a TD-DFT
calculation (Functional B3LYP; basic set, 6-31G (d, p) shows that
the energy gap .DELTA.E (.sup.1CT-.sup.3CT) for the optimized
triplet geometry is 8 cm .sup.-1 (1 meV). Thus, example molecule 4
represents an organic molecule of the invention.
[0094] The chemical synthesis of the example molecule 4 started
from commercially available starting materials is explained in the
following Scheme.
##STR00020##
Example 5
##STR00021##
[0095] Example Molecule 5
[0096] Calculation for the sample molecule 5 in a TD-DFT
calculation (Functional B3LYP; basic set 6-31G (d, p)) shows that
the energy gap .DELTA.E (.sup.1CT-.sup.3CT) for the optimized
triplet geometry is 9 cm.sup.-1 (1.1 meV). Thus, example molecule 5
represents an organic molecule of the invention.
[0097] The chemical synthesis of the molecule example 5 started
from commercially available starting materials is explained in the
following Scheme.
##STR00022##
Example 6
##STR00023##
[0098] Example Molecule 6
[0099] Calculation for the sample molecule 6 in a TD-DFT
calculation (Functional B3LYP; basic set, (6-31G (d, p) shows that
the energy gap .DELTA.E (.sup.1CT-.sup.3CT) for the optimized
triplet geometry is 12 cm.sup.-1 (1.5 meV). Thus, example molecule
6 represents an organic molecule according to the invention.
[0100] The chemical synthesis of the molecule example 6 started
from commercially available starting materials is explained in the
following scheme.
##STR00024##
[0101] FIG. 13 shows another example molecule of the invention.
FIGURE
[0102] FIG. 1: Energy level diagram illustrates the process of
thermally activated delayed (delayed) fluorescence (TADF). k.sub.B
represents the thermal energy k.sub.B of the Boltzmann constant and
T is the absolute temperature. The diagram shows the radiative TADF
process, observed at low temperature and non-radiating (wavy)
deactivation from the T.sub.1 state. The process of spontaneous
S.sub.1.fwdarw.S.sub.0 fluorescence is not shown in the
diagram.
[0103] FIG. 2: Influence of polarity of the solvent on the energy
position of the .sup.1CT-emission for the dissolved sample molecule
1 at T=300 K. The figure shows the red shift of the emission
spectra with increasing polarity of the solvent (quantified by the
dielectric constant .epsilon.).
[0104] FIG. 3: Isosurfaces of the frontier orbitals for the sample
molecule 1 (see example 1), HOMO: left, LUMO: right. Geometry
optimizations were carried out for the electronic ground state
S.sub.0. Calculation methods: DFT and TD-DFT, Functional: B3LYP,
basic set: 6-31G (d, p), calculation software: Gaussian 09. The
calculations show the energy gap between the singlet CT state and
the triplet-CT state is 7 cm.sup.-1 (T.sub.1 geometry). This value
indicates that example 1 is a good emitter for use in
optoelectronic devices.
[0105] FIG. 4: Perspective view of example molecule 1, resulted
from an X-ray structure determination. The single crystal used for
structure analysis was performed by slow diffusion of hexane into a
saturated dichloromethane solution of 1.
[0106] FIG. 5: Emission and excitation spectrum of example
substance 1 dissolved in toluene (c.apprxeq.10.sup.-5 M). The
residual oxygen was removed from the solution by passing nitrogen
over 120 minutes. The emission quantum yield was .PHI..sub.PL=65%.
Excitation: 310 nm, detection: 468 nm.
[0107] FIG. 6: TADF decay time of the sample molecule 1 dissolved
in toluene and nitrogen-purged (T=300K, c.apprxeq.10.sup.-5 M).
Excitation: 310 nm, pulse duration: 10 ns. The measured value of
.tau.=420 ns represents the shortest decay time, which is
significantly shorter than the previously measured TADF shortest
decay time.
[0108] FIG. 7: (a) Emission spectrum of example molecule 1 in
diethyl ether (c.apprxeq.10 .sup.-5 M). The emission represents the
.sup.1CT-fluorescence equilibrated with the .sup.3CT state with a
decay time of .tau.=960 ns (b). The sample was purged with nitrogen
for 120 minutes. Excitation: Spectrum (a): 310 nm (cw-LED); Decay
curve (b): 310 nm (LED pulsed). Temperature (T)=300 K.
[0109] FIG. 8: Emission spectrum of example molecule 1 in a fixed
TADF matrix (see text) (c.apprxeq.10 wt. %). The emission
represented a fluorescence equilibrated with .sup.3CT-state with a
decay time of 530 ns. The sample was carefully degassed.
Excitation: 310 nm (cw-LED). Temperature (T)=300 K.
[0110] FIG. 9: Emission spectra of example molecule 1 in a fixed
TADF matrix (see text) (c.apprxeq.10 wt. %) at various temperatures
(spectra normalized). The emission spectra vary only slightly with
cooling. The decay times are extended from 530 ns (300 K) to
.apprxeq.1 us (10 K). The radiative rate changes only slightly with
cooling.
[0111] FIG. 10: Energy level diagram for explaining the emission
behavior of the example molecule 1 in a polar matrix, such as
diethyl ether or the above-described TADF matrix. The localized
.sup.3LE state is energetically above the .sup.1,3CT states. The
states can comprise quantum mechanical mixtures, namely the
.sup.3LE-state and the .sup.1CT-state can be mixed by spin-orbit
coupling (SOC), while the two triplet states can interact through
configuration interaction (CI). This result is in a rapid
intersystem crossing (ISC) between the .sup.1CT and the .sup.3CT
state. As a result, even at low temperature, only
.sup.1CT-fluorescence equilibrated with the .sup.3CT state can be
observed, neither a .sup.3CT phosphorescence, nor a TADF.
[0112] FIG. 11: Isosurfaces of the frontier orbitals for the sample
molecule 2 (see example 2.), HOMO: left, LUMO: right. Geometry
optimizations were carried out for the electronic ground state
S.sub.0. Calculation methods: DFT and TD-DFT, Functional: B3LYP,
basic rate: 6-31G (d, p), Calculation software: Gaussian 09. The
calculations predict 5 cm.sup.-1 (0.6 meV) (S.sub.0 geometry) for
the energy difference between the singlet CT state and the
triplet-CT state.
[0113] FIG. 12: Isosurfaces of the frontier orbitals for the sample
molecule 3 (see example 3.), HOMO: left, LUMO: right. It made
geometry optimizations for the electronic ground state S.sub.0.
Accounting methods: DFT and TD-DFT, Functional: B3LYP, basic rate:
6-31G (d, p), invoice Software: Gaussian 09. The calculations
predict for the energy gap between the singlet state and the
triplet CT-CT state 5 cm .sup.-1 (S.sub.0 (0.6 MeV) geometry).
[0114] FIG. 13: Further examples of the invention organic emitter
molecules that are suitable for the usage in opto-electronic
devices.
* * * * *